The present invention relates to integrated circuits, and more particularly, to a complex device that is hard to duplicate.
The large diffusion of the so-called xe2x80x9csmart-cardsxe2x80x9d for applications such as credit cards, medical record memory cards, electronic driver licenses, etc. require that data stored in such integrated devices be very secure. Both hardware and software used in these devices must be designed and formed in such a way as to satisfy this need of protection.
Sophisticated xe2x80x9creverse engineeringxe2x80x9d techniques are known and used, often illegally, to duplicate integrated circuits from commercially available samples. This causes a great economic loss to the company that designed them.
It is important to make if difficult to duplicate such integrated circuits, even through reverse engineering techniques that include microscopic inspection of the integrated circuit being duplicated. Making it difficult to duplicate integrated circuits is applicable whether the devices are intended for applications in which it is particularly important to keep stored data undecipherable, or whether the devices result from a long and expensive development process.
Making the hardware system secure may represent an insuperable obstacle to the identification of working codes, i.e., hardware protection in addition to the software ciphering of stored data. Known reverse engineering techniques can be used to duplicate an integrated circuit when inspected by an optical or electronic microscope.
In view of the foregoing background, an object of the present invention is to make it very difficult to reverse engineer integrated circuits, such as smart cards, using visual and even destructive inspection techniques.
This and other objects, advantages and features according to the present invention are provided by anti-deciphering contacts for integrated devices in which a plurality of false contacts and/or false interconnection vias are formed in a way to make them totally indistinguishable from true contacts and true interconnection vias, even by a destructive inspection of the device. False contacts and false interconnection vias are connected like true contacts and true interconnections vias by metal lines defined in a respective layer of conducting material.
True contacts and true interconnection vias extend throughout the entire thickness of an insulating dielectric layer or multilayer to reach and establish electrical paths with the respective active area in the case of contacts, or with another conducting element of the integrated structure in the case of interconnection vias. False contacts and false interconnection vias are formed using a dedicated mask, complementary to the mask of true contacts or true interconnection vias, and extend only partially through the thickness of the respective insulating dielectric layer or multilayer. The false contacts and false interconnection vias thus remain as electrically isolated xe2x80x9cappendicesxe2x80x9d without any function.
False contacts and false vias in accordance with the present invention do not establish any current path even if they are at the potential of the circuit node to which they are connected through the respective metallization lines that intercept them. The only way of determining their false nature would be to section the device for establishing a path for each contact and each interconnection via, whether it is true or false. This would be a very burdening job requiring someone to buy and sacrifice a very large number of identical devices.